# Gauss (TA Luft 86)

### Coarse Mesoscale Dispersion Estimation

Gauss ^{TA Luft'86} is the implementation of a simple Gauss model to get a quick estimation about pollutant concentrations.

The model was designed for source heights > 10 m above ground and free flow between source and receiver. Therefore, it can only be used exceptionally and with expert knowledge to calculate ground near pollution sources.

### Preparation

- The SoundPLAN Meteorological Station Library helps to analyze meteorological data visually, adjust them to your task and to calculate or derive Klug/Manier stability classes. Special TA Luft classification settings support short calculation time.
- The time histogram library helps to create and store cyclical time variant emission source parameters addressing each single hour of a year. Alternatively ASCII-lists can be used to take non-cyclic time variant emissions into account.

### Data Input

- SoundPLAN Geodatabase allows importing, digitizing and editing model data via several interfaces or just to use models prepared for SoundPLAN noise calculations. Background bitmaps can be used, e.g. geo-referenced aerial photos.

### Calculation

- The SoundPLAN calculation kernel offers a user friendly interface to define the Gauss
^{TA Luft`86}calculation settings. Run control is supported by a graphical result display which is successively updated until the calculation is finished. Several kernels can be used parallel for each calculation run. With module Distributed Computing several computers can be driven parallel.

### Presentation

- The SoundPLAN Graphics module assists preparing outstanding presentation graphics. Even more, it allows also to modify data in a post processing by user defined formulas or to combine results. E.g. for a MISKAM calculation it can be sensible to add a Gauss
^{TA Luft'86}background pollution map.

# Model Description

### Origin

The Gauss model is based on the formulas of the German standard TA Luft`86, Appendix C, which was initially designed and validated for licensing proceedings of industrial chimneys higher than 10 m above ground and at least 3 m above the roof tops. However, it was also (carefully) used for ground near sources, e.g. doing smell prognosis for livestock.

### Model type and field of application

Gaussian models are based on easy formulas to describe the statistical relation between source emission and concentration at a receiver point within a generalized plume shape. Obstacles and terrain are not regarded. Therefore, they are very quick in calculation, even if you calculate results for many sources and receptor points, like a grid map.

SoundPLAN emission sources (point, line, area and road sources) are automatically replaced by point emission sources, because the Gauss model formula only knows point sources and receptor points. The resolution of substitute sources is dynamical adjusted to the distance source <> receiver. Grid maps are defined by a free shaped calculation area polygon, horizontal grid space and height above ground.

Our Gauss model is a simple one with few parameters for coarse estimations. Experience is required to assess the reliability of Gauss model results, because simple models don’t automatically calculate on the safe side in any case, as many people think.

We think, Gauss models are no longer state-of-the-art and serious studies should be done with one of our more complex model types. Especially results for high percentiles, in nature caused by extreme constellations, are not very close to reality, because in the Gauss model they are derived from an ideal Gaussian distribution.

### Time Resolution and meteorology

For quick calculation of annual means use three dimensional dispersion class statistics based on at least hourly measurement. Created in the SoundPLAN Meteorological Station Library they contain the frequency for each combination of 6 Klug/Manier stability classes, 9 wind speed classes and 36 wind direction sectors.

Alternatively hourly time series of meteorological measurement regard time variant emissions and time variant effective source height parameters. Stability information must be available as Klug/Manier classes, which can be calculated or approximated by several approaches within the library.

### Spatial Resolution

The horizontal resolution is typically between 10 meters and some hundred meters up to some kilometers. First the reliability of results grows with increasing distance between source and receptor, but after a certain size of the investigation area it must be questioned, how much time the pollutants need to leave this area and if a static plume can be assumed to be representative for this whole time.

As there is no wind field calculated, the spatial resolution has no direct influence on the dispersion results. However, coarse grids flatten local peaks in comparison with fine grids, if small local peaks are not met by the receiver grid.

### Emission Sources

The SoundPLAN interface offers point- line- and area emission sources, also roads. Line and area sources can be freely shaped polygons. Road sources are offered as separate object type for graphics etc. Time variant emissions can be regarded from simple day histogram cycles up to completely non-cyclic year histograms like weather dependent emissions, when there is an hourly measured meteorological time series available.

Effective source height can be calculated as thermal upstream for point sources.

### Pollutants

The pollutant list is completely user defined. It can contain any desired neutral gas and dust in 4 grain size classes.

Reactive NOx is dispersed like a non reactive gas and the NO2-concentrations can be derived from the NOx concentrations using one of several offered approaches or using own conversion formulas.

### Topography

Topography is not regarded.

### Buildings, Obstacles, Landuse

Undisturbed wind flow at the emission source is required. Buildings and land use effects are not explicitly regarded. Roughness can be roughly regarded if the Klug/Manier stability classes are calculated from cloud covering.

### Available results

Mean value and free definable percentiles for the selected time period (defined by the weather statistics you use). Single point receptors can be used to create result tables. A freely shaped calculation area polygon can be used to create a concentration grid map. Results display concentrations in receiver height and deposition on the ground.

### Support

The model equations are state of the TA Luft'86. The interface is steadily adjusted to the current SoundPLAN versions, including steadily improved tools in the program environment (meteorology, background measurement analysis etc.) but there is no further formula development. We give hotline support for the correct implementation of the formulas and the interface.

### Note

Gauss models are simple models, but they require good background knowledge. You have to interpret results correctly. As Gauss deals with flat terrain and ignores obstacles, you have to know how these limitations influence your results.